Concrete is a commonly used building material. Forms are fashioned and concrete is poured into the forms to harden, and then the forms are removed. To reinforce the concrete, a grid of metal "rebar" rods may be placed within the forms so that when the concrete hardens, it is strengthened by the rebar. The grid can be formed by a set of horizontal rebar rods which intersects with a set of vertical rebar rods. To hold the rebar grid in place, it is common to tie off the cross joints of the intersecting horizontal and vertical bars with a wire. This is a time-consuming process when done by hand, using standard 16 gauge annealed wire (about 67,000 psi).
A conventional hand tie, using pliers or similar tool, involves looping a strand of wire over a cross joint and pulling it tight so that the loop tightly encloses the joint with the ends of the wire twisted off to prevent unraveling. Two complete twists of 360 degrees each will hold the tie in place. Sometimes the wire is doubled to prevent the wire from breaking at the tie/twist point.
Because the tied joint has to hold while concrete is subsequently poured over it into the form, and may also (when the rebar is preassembled off-site) have to hold securely while the rebar grid is lifted, moved, stepped on, and handled, the wire tie must be tight and strong. Because of the difficulties associated with hand tying, it would be desirable to develop a light weight, portable, and reliable mechanical wire-tying tool.
A desirable mechanical wire-tying tool should be able to:
(a) loop a strand of wire over the joint to be tied--for this purpose a movable set of talons may be used with the talons placed over the joint and closed, the wire fed through the talons, and the wire then released from the talons so as to form a loop over the joint; PA1 (b) cut and twist the ends of the wire looped over the joint--for this purpose a spinner/cutter may be used to cut the ends of the wire loop, to hold the loop under tension, and to twist the ends so as to form a "knot" without breaking the wire before the knot is formed, and drawing out the cut off ends of the wire loop as the knot is formed to leave the tie in place; PA1 (c) pull back the slack on the ends of the loop after it is placed over the joint and then keep the loop under tension as the ends are twisted and the knot is being formed so as to form a tight knot--for this purpose, some sort of pullback mechanism and tension device should be used; and PA1 (d) feed a hard wire through the device without misfeeding through the talons or otherwise--for this purpose, a heavy duty wire drive mechanism should be used, and other portions of the device should be designed so as to cooperate in order to handle a hard wire delivered at high speed.
A desirable mechanical wire tying machine should be able to accomplish all of the foregoing functions rapidly and reliably with a hard wire, and should be capable of being operated by a single person. Prior art mechanical wire tying tools have not been completely satisfactory in meeting all of the desired features.
U.S. Pat. No. 3,391,715 of Thompson and U.S. Pat. No. 5,217,049 of Forsyth show wire tying devices having talons that are movable; cutters that include clamps with shear-plates (a shear disk); and feeding systems with a standard, paired wheel friction drive. Pullback is accomplished by reversing the drive wheels.
Other variations on a device having a talon, and including shear disk cutters (or a moveable disk cutter or a single blade "loper"), conventional feeding systems such as standard paired wheel friction devices, or drive wheel reversal for pullback are shown in U.S. Pat. No. 4,362,192 of Furlong et al.; U.S. Pat. No. 4,117,872 of Gott et al.(double wire system with talons that are channeled and not fully enclosed); U.S. Pat. No. 4,354,535 of Powell et al. (open groove); U.S. Pat. No. 4,685,493 of Yuguchi; U.S. Pat. No. 4,953,598 of McCavey (single hook, open groove); and U.S. Pat. No. 4,834,148 of Muguruma et al. (open groove with semi-enclosing member).
U.S. Pat. No. 4,542,773 of Lafon describes a wire tying machine with two lower jaws. Hand powered wire tie machines are shown in U.S. Pat. No. 5,178,195 of Glaus et al. and U.S. Pat. No. 3,593,759 of Wooge.
A principal disadvantage of current mechanical wire tying devices is their inability reliably to replace hand tying. The wire often misfeeds through the talons. The ends of the looped wire are frequently not twisted under tension sufficient to create a tight knot, and/or the knot breaks as it is being spun. The feed systems may not support a rapid advancement of a relatively hard wire, nor do the pullback or spools take up the wire.
It can be seen that there is a need for a reliable mechanically assisted wire tying tool. Preferably, the tool would include enclosed or partially enclosed talons for channeling a loop of relatively hard wire around a rebar joint at high speed, a pullback feature to retract the loop under tension to tighten the loop around the joint, a spinner/cutter that extrudes a knot by turning, kinking, and cutting the wire (holding the cut ends under tension) and then spinning in complete revolutions to twist the wire into a knot while drawing the spinner away from the work surface (so as not to break the knot as it is being formed), and a reset control to immediately reset the tool for the next tie.
The complete cycle should be completed in the space of about 2 to 3 seconds. The tool should be hand held and driven by electricity or compressed air. It should weigh around 15 to 20 pounds, be about 18 to 24 inches long, and about 4 to 6 inches in diameter. The tool should be able to improve upon the standard 16 gauge annealed wire rated at approximately 67,000 psi and which is commonly used in hand tied knots, by handling, instead, a much harder wire, such as a 16 gauge "green" (nonannealed) hard wire rated above 67,000 psi and up to approximately 127,000 psi, or greater.
It is a specific object of the wire tying apparatus and method of this invention to provide those benefits of reliability and performance which will permit a power tool to replace hand tying.